Snow melt system for solar collectors

ABSTRACT

A solar collector system having several evacuated tube solar collectors arranged together, a conductor arranged on the solar collectors, a power source for sending electricity through the conductor, and an indicator connected to the conductor to indicate when electricity is flowing through the conductor. A snow sensor connected is connected to the conductor adjacent the evacuated tube solar collectors and a controller is connected to the snow sensor. The controller controls the electricity flow through the conductor and allows electricity to flow when the snow sensor senses snow covering the snow sensor, and stops the electricity flow when the snow sensor is no longer covered. The electricity flow heats the conductor, which in turn melts the snow on the collectors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 USC 119(e) of U.S. Provisional Application Ser. No. 61/616,701, filed on Mar. 28, 2012.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a snow melt system for solar thermal collectors, particularly evacuated tube collectors. In particular, the invention relates to a snow melt system having heated wires running around the evacuated tubes, to prevent snow from adhering to the collectors and decreasing their efficiency.

2. The Prior Art

Solar collectors are used throughout the world to convert solar energy into hot water. There are two different types of solar collectors, flat plate and evacuated tube. These two types are different in structure, but have the same purpose. Both act as renewable resources for domestic hot water (DHW) by using the sun's rays to heat up the heat transfer fluid (HTF). A flat plate collector has a series of vertical finned tubes connected by the HTF inlet at the bottom and the HTF outlet at the top. All of the finned tubes are covered by a single flat plate of glass. In an evacuated tube collector, he tubes are mounted, with the condenser bulbs up, into a heat exchanger (manifold). The manifold is a shaped copper pipe that wraps around both sides of each condenser bulb. Potable water from the recirculation loop flows through the manifold and picks up heat from the condenser bulbs. The maximum operating temperature of the heat pipe is the critical temperature of the dual-phase fluid, since no evaporation or condensation above the critical temperature is possible. The heat pipe also provides the system with a thermal diode function, so that when the sun is not shining, heat loss from the potable water is kept to a minimum. This occurs because heat is lost only from the header, not from the absorber surface of the array. The header is insulated with polyurethane foam to a U-value of 0.28 to 0.35 W/m K. Within each condenser bulb, the maximum working temperature is controlled by means of memory-metal snap discs to a level below the critical temperature.

The memory metal is programmed to change its shape at a preset temperature. This allows the condenser fluid to be retained inside the condenser. When the programmed temperature is reached, the memory-metal spring expands and pushes a plug against the neck of the heat pipe, blocking the return of the condensed fluid and stopping latent heat transfer. At temperatures below the maximum programmed limit, the spring contracts, allowing the condensed fluid to return to the lower section of the heat pipe. The solar heat from the absorber plate then causes the condensate to evaporate, transferring thermal energy to the condenser. Because of the difference in their structure, evacuated tubes perform more efficiently in a typically cool, cloudy, or snowy environment, but for the same reason, snow can keep evacuated tube collectors from performing to their full potential efficiency. Because an evacuated tube collector has rows of individual glass tubes that do not radiate much heat, the tubes tend to build up and collect a lot of snow, like a snow fence, rather than shed it. Even though each collector is covered by glass and is transparent, some light is still reflected. When covered by snow the tubes obviously become more opaque and do not allow for very much light to pass through it, affecting its efficiency. This accumulated snow can thus greatly reduce the efficiency of the energy transfer.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a system for preventing and eliminating snow accumulation on an evacuated tube solar collector system. This object is accomplished by providing a solar collector system having at least one evacuated tube solar collector, a conductor arranged on the solar collector, a power source for sending electricity through the conductor, and an indicator connected to the conductor to indicate when electricity is flowing through the conductor. The conductor is preferably formed from a material that heats up quickly when electrical current is applied to it. A snow sensor connected is connected to the conductor adjacent the evacuated tube solar collector and a controller is connected to the snow sensor. The controller controls the electricity flow through the conductor and allows electricity to flow when the snow sensor senses snow covering the snow sensor, and stops the electricity flow when the snow sensor is no longer covered. The electricity flow heats the conductor and melts the snow on the collector. Preferably, there are a plurality of evacuated tube collectors arranged together, and the conductor is arranged on all of them.

In one embodiment of the invention, the conductor is a wire. The wire is preferably arranged in a serpentine pattern around a circumference of each of the solar collectors. Other patterns could also be used. The wire can be located around the outside of the solar collector, or can be embedded within the solar collector. The wire could be made of any suitable material, such as Nichrome. Nichrome is a non-magnetic alloy of nickel, chromium and sometimes iron. Nichrome is particularly suitable due to its high electrical resistivity and resistance to oxidation at high temperatures.

In another embodiment, the conductor is a conductive paint that is applied to the surface of each of the evacuated tube collectors.

The indicator can be any type of indicator, such as a Light Emitting Diode (LED).The power source can be any suitable power source. For example, the power source could be a photovoltaic panel connected to a charge controller and a battery.

The snow sensor could be any commercially available snow sensor, such as those made by Tekmar or Thermon. These sensors contain a moisture sensing component and an air temperature sensor so that when the air temperature falls below a certain threshold and the moisture sensing component senses moisture, a switch on the sensor is activated to alert the controller to turn on the snow melt system.

The present invention provides a particularly efficient and simple way to keep snow from accumulating on the solar collectors. The use of a PV panel as the power source ensures efficient operation of the system. The amount of power generated by the PV panel is sufficient to ensure adequate snow melt on the collector array. As an alternative or in addition, the power could be supplied directly from a house or a building's 110 v or 220 v power system, using a transformer. The house supply could be used as a backup for the PV panel, in case there is insufficient sunlight to power the system using solely the PV panel.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

In the drawings, wherein similar reference characters denote similar elements throughout the several views:

FIG. 1 shows an exploded view of the snow melt system according to the invention;

FIG. 2 shows a view of a single evacuated tube solar collector used in the system according to the invention;

FIG. 3 shows an example of a snow melt sensor for use in the system according to the invention; and

FIG. 4 shows a block diagram of the system according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now in detail to the drawings and, in particular, FIG. 1 shows the snow melt system 10 according to the invention. System 10 comprises an evacuated tube solar collector array 20 comprised of individual evacuated tube solar collectors 21 arranged on a rack 22. Arranged on each solar collector is a conductor 23 which can be in the form of a wire or conductive paint. Conductor 23 is connected to a controller 30, which controls the electricity supplied to conductor 23. Controller 30 is connected to battery 31 and stored in a waterproof housing 32. Battery 31 is powered by photovoltaic panel 33, which turns solar energy into electrical current. Panel 33 can be configured of various sizes, depending on the size of the array 20 and amount of snow to be melted.

A snow sensor 35 is attached adjacent array 20 to sense the presence of snow on array 20. Sensor 35 is connected to controller 30.

FIG. 2 shows an enlarged view of a single evacuated tube solar collector 21. Collector 21 comprises an evacuated glass tube 24 in which conductor 23 is embedded. Conductor 23 is a wire embedded within the glass of tube 24. An evacuated heat pipe 25 is disposed inside tube 24 and extends into a copper manifold 26. Inside manifold 26 is disposed insulation 27, and a copper sleeve 28 into which heat pipe 25 extends. Heat pipe 25 is encased in an aluminum head casing 29. Heated water circulates through manifold 26, heated by heat pipe 25, which is heated by the sun. When snow 40 collects on collector 21, sensor 35 senses snow 40 and causes controller 30 to send electricity through conductor 23 to melt snow 40. Conductor 23 can be made of wire or conductive paint.

Snow sensor 35 is shown in detail in FIG. 3. Sensor 35 contains a moisture sensor 36 and a temperature sensor 37. Sensor 35 is connected via lines 45 to controller 30. When temperature sensor 37 senses a temperature below a threshold level, such as 32° F., and moisture sensor 36 senses a threshold level of moisture, snow sensor 35 sends a signal to controller 30 to send power to conductor 23.

A circuit diagram of system 10 is shown in FIG. 4. As can be seen there, conductor 23 is arranged in a serpentine pattern along each collector 21 and is connected to controller 30, which can be a microprocessor, through switch 38. A photovoltaic panel 33 supplies energy to battery 31 through charge controller 34. Panel 33 varies from 0-18 VDC and charge controller 34 controls the voltage to keep the voltage to battery 31 to no greater than 14 VDC. Electricity from battery 31 runs to conductor 23. Snow sensor 35 is also connected to controller 30 so that when snow sensor 35 senses snow, controller 30 causes switch 38 to close and send electricity through line 42 to conductors 23 on collectors 21. A variable resistor 39 is arranged in line 42 to control the amount of current supplied to conductors 23. A temperature sensor 45 is arranged near collectors 21 so that when sensor 45 senses a temperature above a preset threshold temperature, controller 30 opens switch 38 to cut power to conductors 23. This prevents the system from overheating and damaging the collectors and the rest of the system.

The system is set up so that each conductor 23 is wired in parallel. This allows lines 43 and 44, which connect each individual conductor 23 to lines 42 and 47, to be easily disconnected from each conductor 23. This way, damaged collectors 21 can be easily replaced without dismantling the system. The system could also be wired in series.

An indicator 36 is connected to controller 30. Indicator 36 can be a Light Emitting Diode (LED) or any other type of suitable indicator. Indicator 30 illuminates when power is supplied to conductors 23, and turns off when the power is cut.

Power supply 47 can be connected to the system as well, to be used as a backup in case PV panel 33 does not supply sufficient power, due to lack of sunlight.

Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A solar collector system comprising: at least one evacuated tube solar collector; a conductor arranged on the solar collector; a power source for sending electricity through the conductor; an indicator connected to the conductor to indicate when electricity is flowing through the conductor; a snow sensor connected to the conductor and being disposed on or adjacent to the at least one evacuated tube solar collector; and a controller connected to the snow sensor, and conductor said controller controlling the electricity flow through the conductor and allowing electricity to flow when the snow sensor senses snow, and stopping the electricity flow when the snow sensor does not sense snow.
 2. The system according to claim 1, wherein the conductor is a wire.
 3. The system according to claim 2, wherein the wire is arranged in a serpentine pattern around a circumference of the solar collector.
 4. The system according to claim 2, wherein the wire is made of Nichrome.
 5. The system according to claim 1, wherein there are a plurality of said solar collectors and wherein the conductor is arranged around each of the solar collectors.
 6. The system according to claim 1, wherein the indicator is a Light Emitting Diode (LED).
 7. The system according to claim 2, wherein the wire is embedded within each solar collector.
 8. The system according to claim 1, wherein the conductor is a conductive paint applied to each solar collector.
 9. The system according to claim 1, wherein the power source is a photovoltaic panel connected to a charge controller and a battery.
 10. The system according to claim 1, further comprising a temperature sensor connected to the conductor and to the controller, wherein the controller is adapted to stop the electricity flow through the conductor when the temperature sensor senses a temperature above a predetermined threshold level.
 11. The system according to claim 1, wherein the controller is a microprocessor. 